Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.61	7.429%	$90.8957	$90.90	$90.90	$90.90
Purchase #2	$26.85	3.301%	$27.7363	$27.74	$27.75	$27.70
Purchase #3	$163.78	10.620%	$181.1734	$181.17	$181.15	$181.20
Purchase #4	$99.40	4.426%	$103.7994	$103.80	$103.80	$103.80
Purchase #5	$18.94	6.639%	$20.1974	$20.20	$20.20	$20.20
Purchase #6	$74.79	3.257%	$77.2259	$77.23	$77.25	$77.20
Purchase #7	$134.34	4.636%	$140.568	$140.57	$140.55	$140.60
7 purchase totals =	$602.71		$641.5961	$641.61	$641.60	$641.60